Tires are occasionally punctured by hard objects, such as nails, stones, etc, on road. Flattening of the tires is resulted due to air-leaking through the puncture. It could cause serious accident and severe physical injure to the drivers, particularly when the car is running on highway. Additional accident occasionally happened when the driver attempted to replacing the flattened tire in highway network.
Liquid tire sealant is used for sealing of tire puncture temporarily when the tires are in operation. This provides an emergency measure for the driver to continue the journey and seek for help even after the tire is punctured so as to prevent any serious accident to be happened due to the tire flattening.
In general, a liquid tire sealant consists of sealing materials, tackifier and solvent with anti-freezing agent. The common sealing materials include latex, butyl rubber and various particulates. Tackifiers are chemicals used for increasing the tackiness. A common tackifier used for tire sealant is resin compound. Anti-freezing agent, such as ethylene glycol and propylene glycol, is used to lower the freezing point of the tire sealant in order to prevent the sealant from freezing at low temperature operating environment.
In the early stage of tire sealant development, as described in U.S. Pat. Nos. 4,116,895 and 4,426,468, butyl rubber and latex were used as the main components for sealing purpose. As cross-linking agents (i.e. organometallic catalysts) were needed for the proper function, the sealing ability is highly sensitive to the amount of catalyst. The drawbacks of these compositions include unstable performance, short shelf-life, difficulty to clean up after usage and requirement of curing process.
U.S. Pat. Nos. 4,337,322 and 4,588,758 described the further development of tire sealant. These patents disclosed the use of asbestos fiber, ethylene glycol and detergent as main components in the valve-open type sealant. It is well known that asbestos fiber is carcinogenic whereas ethylene glycol is toxic to environment.
In light of the environmental concerns, a non-petroleum based, environmentally safer tire sealant was disclosed (U.S. Pat. No. 5,059,636). In the formulation, in addition to ground rubber, wheat flour was used. Sodium nitrite was used as preservative for longer shelf-life. On the other hand, freezing point of the aqueous sealant solution was lowered by addition of calcium salt instead of glycol compound. The only drawback is that the valve core needed to be removed before applying the sealant.
Instead of water-based tire sealant, formulations with organic propellants were developed (U.S. Pat. Nos. 490,242 and 5,648,406) through the use of halogenated compounds and other organic solvent such as acetone are potentially hazardous to the environment despite of their high sealing performance.
At the mean time, another sealant formula was purposed in U.S. Pat. No. 5,772,747. The sealant functions based on the mechanism called “log-jam”. Indeed, mixture of particles including cellulose, xanthan gum, carbopol polymer, wool, nylon, rayon, wollastonite and other flat plate-like particles were suspended in water-based solvent. A tire puncture can be filled up by the fibrous materials in a viscous medium, tuned by addition of polyglycol. Propylene glycol was added to lower down the freezing point of the sealant. Other constituents including colouring, preservative and anti-corrosion additives were added.
With similar functional mechanism, sealant formulation consisting of surface activated ground rubber, styrene butadiene latex, polysaccharide Xanthan gum was disclosed (U.S. Pat. No. 5,856,376). Nevertheless, it was still valve-open type sealant.
In U.S. Pat. No. 6,013,697, bentonite clay and mica were used as the main constituents in the disclosed formulation. These particulates filled the puncture voids and formed a clog to prevent further air leak. The valve-through type sealant was environmentally safe and it has quick sealing performance. However, settling and flocculation of clay platelets were the main issues for this sealant.
Other works based on the log-jam mechanism mainly used natural organic materials include US 2002/0077391 A1 in which chopped polyethylene, cellulose, and ceramic fibers were used; US 2005/0277712 A1 in which by-products of crop such as sugar beets, sugar cane, corn and timber were used as the particulates; International Patent WO 2008/022402 A1 in which the sealant contained Xanthan gum, cellulose, fumed silica, peanut shell, bark powder, tea powder, parsley powder, bentonite, gum resin and trace titanium dioxide; US 2007/0015850 A1 in which plant protein such as cereal grains, corn and wheat were used; US 2007/0129464 A1 mentioned the use of fiberous materials including molasses, i.e. cane, sugar beet, corn, soybean, lignin, wool, glass wool, cotton, etc.
Other works based on the log-jam mechanism mainly used synthetic materials include US 2007/0203260 A1 in which urethane emulsion (synthetic resin) and polyols were used; International application number PCT/AU2008/001499 in which sodium polyacrylate and ground rubber were the main components of the disclosed tire sealant.
In addition to the “log-jam” principle, another type of sealants was based on tackified latex suspension. The latex suspension was a highly viscous liquid that could adhere on the puncture wall firmly and eventually blocked the air leaking channel. The related patents include but not limited to EP 1382654 A1, U.S. Pat. No. 6,992,119 B2 and US 2006/0142420 A1. However, the disadvantages of latex-based sealant were difficulty to clean after usage, problematic sticky nature, irritation to eyes and skins, use of volatile organic compounds, etc.